1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful formicrofabrication utilizing various types of radiation such as ultraviolet rays, deep ultraviolet rays, X-rays, or charged particle rays.
2. Description of Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, the processing size has become more and more minute in order to achieve higher integration. In recent years, development of a lithographic process enabling stable microfabrication with a line width of 0.5 xcexcm or less has been strongly demanded.
However, it is difficult to form such a fine pattern with high accuracy using a conventional method which utilizes visible rays (wavelength: 700-400 nm) or near ultraviolet rays (wavelength: 400-300 nm). To deal with this problem, a lithographic process using radiation with a shorter wavelength (wavelength: 300 nm or less) has been proposed. Such shorter wavelength radiation can achieve a wider range of depth of focus and is effective for ensuring design rules with minimum dimensions.
As examples of shorter wavelength radiation, deep ultraviolet rays such as a KrF excimer laser (wavelength: 248 nm) or an ArF excimer laser (wavelength: 193 nm), X-rays such as synchrotron radiation, charged particle rays such as electron beams, and the like can be given. International Business Machines Corporation (IBM) has proposed a xe2x80x9cchemically-amplified resistxe2x80x9d as a resist exhibiting high resolution for such shorter wavelength radiation. At present, improvement of the chemically amplified resist has been attempted.
The chemically-amplified resist contains a photoacid generator which generates an acid upon irradiation (hereinafter called xe2x80x9cexposurexe2x80x9d). Chemical changes in the resist coating (changes in polarity, breakage of a chemical bond, cross-linking reaction, etc.) caused by the catalytic action of an acid changes solubility of the exposed area in a developer. The resist pattern is formed utilizing this phenomenon.
In the chemically-amplified resist, the photoacid generator greatly affects functions as a resist. In these days, onium salt compounds, which generate an acid upon exposure in high quantum yield and exhibit high resolution, are widely used as the photoacid generator. The onium salt compounds contain an onium cation and a counter anion. The structure of the onium salt compounds has been extensively studied.
Among the resin components used in conventional chemically-amplified resists, the following resins are known as those exhibiting comparatively good resist performance: a resin in which an alkali affinitive group in an alkali-soluble resin is blocked by a t-butyl ester group or a t-butoxycarbonyl group (Japanese Patent Publication No. 27660/1990); a resin in which an alkali affinitive group in an alkali-soluble resin is blocked by a ketal group (Japanese Patent Application Laid-open No. 140666/1995); a resin in which an alkali affinitive group in an alkali-soluble resin is blocked by an acetal group such as an ethoxyethyl group and a tetrahydropyranyl group (Japanese Patent Applications Laid-open No. 161436/1990 and No. 249682/1993); a combination of a resin in which an alkali affinitive group in an alkali-soluble resin is blocked by a t-butoxycarbonyl group and a resin in which an alkali affinitive group in an alkali-soluble resin is blocked by an acetal group (Japanese Patent Applications Laid-open No. 15864/1996 and No. 31309/1998); and the like.
However, all these chemically-amplified resists have peculiar problems. In particular, various problems have been pointed out in putting these resists to practical use for microfabrication with a line width of 0.25 xcexcm or less.
One of the problems is unevenness of the surface of the pattern (surface roughness). A rough surface hinders controlling the line width of the fine pattern with high accuracy. Another problem is that sufficient sensitivity, resolution, and depth of focus cannot be obtained when forming a dense line pattern, isolated line pattern, or contact holes, particularly line-type patterns, which fails to satisfy the requirements for memory circuits, logic circuits, or circuits installing both.
Japanese Patent Application Laid-open No. 167200/1999 discloses a photoresist composition exhibiting good sensitivity which comprises an onium salt compound such as di(4-t-butylphenyl)iodonium perfluorooctanesulfonate and di(4-t-butylphenyl)iodonium 2-trifluoromethylbenzenesulfonate and an alkali-soluble resin such as a 4-hydroxystyrene/styrene/t-butyl acrylate copolymer.
However, Japanese Patent Application Laid-open No. 167200/1999 has a subject still to be investigated, which is a correlation between the onium salt compound and the structure of the alkali-soluble resin in relation to recent major requirements for sensitivity, resolution, depth of focus, and surface roughness in various patterns. Therefore, this photo resist composition is unsatisfactory in view of overall characteristics as the chemically-amplified resist.
Accordingly, an object of the present invention is to provide a radiation-sensitive resin composition which exhibits high sensitivity to various types of radiation such as ultraviolet rays, deep ultraviolet rays, X-rays, and charged particle rays, has sufficient resolution and depth of focus, and is capable of forming a fine pattern with small surface roughness when forming various patterns such as a dense line pattern, isolated line pattern, or contact holes, particularly line-type patterns.
According to the present invention, the above object can be achieved by a radiation-sensitive resin composition comprising:
(A) an aromatic sulfonic acid onium salt compound shown by the following formula (1),
Z+Xxe2x88x92xe2x80x83xe2x80x83(1)
xe2x80x83wherein Z+ represents an onium cation of sulfur or iodine, and Xxe2x88x92 represents an anion shown by any of the following formulas (1-1) to (1-3); 
xe2x80x83and
(B) either one or both of a copolymer (I) which comprises a recurring unit shown by the following formula (2) and a recurring unit shown by the following formula (3), 
xe2x80x83wherein R1 represents a hydrogen atom or a methyl group, R2 represents a halogen atom or an organic group having 1-6 carbon atoms, and i is an integer from 0 to 3; 
xe2x80x83wherein R3 represents a hydrogen atom or a methyl group, R4 represents a tertiary alkyl group having 4-10 carbon atoms, R5 represents a halogen atom or an organic group having 1-6 carbon atoms, and j is an integer from 0 to 3; and
a copolymer (II) which comprises a recurring unit shown by the formula (2) and a recurring unit shown by the following formula (4): 
xe2x80x83wherein R6 represents a hydrogen atom or a methyl group, R7 represents a linear, branched, or cyclic alkyl group having 1-6 carbon atoms, R8 represents a linear, branched, or cyclic alkyl group having 1-6 carbon atoms, R9 represents a halogen atom or an organic group having 1-6 carbon atoms, and k is an integer from 0 to 3.
In the formulas (2) to (4), the organic group having 1-6 carbon atoms excludes xe2x80x94OR4 in the formula (3) and xe2x80x94Oxe2x80x94CH(R7)xe2x80x94Oxe2x80x94CH2xe2x80x94R8.
Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description.